Die cut trays are erected from cardboard or other corrugated sheet material and folded into the desired shape. They are often held in position by appropriately folding and interlocking various parts of the tray. Friction can be used to interlock the parts, but such friction-based locks can fail when the cardboard changes shape through use, wear or from environmental changes. Thus, interlocking parts typically require cutting holes or slots through the tray and inserting parts through the holes and completely through the parts in order to mechanically lock the parts together. But this mechanical interlocking that uses slots weakens the trays in the area where the slots are placed.
The slotted interlocks cause further problems when they are used in some applications. The low cost of these trays makes them suitable for use in mass produced products where the trays assembly can be automated and the trays used on assembly lines. For example, these trays provide an economical way to process and distribute food products, such as cakes and muffins.
A machine forms a die cut tray from a palette of die cut blanks and drops the formed tray onto a conveyor belt. A wax-paper liner is placed on the tray to prevent the food from being absorbed by and sticking to the paper. Batter is poured into the tray for baking, and the batter-filled tray passes through an oven where the cake is baked in the tray. If the shape of the tray changes, the shape of the cake is altered and may render the cake unsuitable for sale. Thus, it is important that the tray holds its shape during the filling and baking process. Further, because thousands of cakes are baked on these automated lines, even a small percentage of trays losing shape or leaking can cause a large loss of money as the baked cakes are much more expensive than the trays. Thus, the tray assembly and the ability to maintain the tray shape must be not only inexpensive, but very reliable.
While the slotted interlocking trays hold their shape, the interlocking slots are typically located on or near the bottom of the tray. The slots thus allow the batter to leak and contaminate the assembly line. Given that tens of thousands of cakes can be baked daily, even a small leakage from a small percentage of trays quickly causes numerous problems, ranging from health and contamination concerns, to equipment maintenance and breakage problems. There is thus a need for low-cost trays that can be inexpensively made, assembled by automated equipment, yet maintain their shape during use and not leak. These objectives must be achieved with a very high repeatability and reliability.